1. Field of the Invention
The present invention relates to prosthetic vascular grafts and, more particularly, to a vascular graft having an exterior texture to promote tissue ingrowth into the graft to enhance fixation and, inter alia, preclude perigraft leakage.
2. Discussion of the Related Art
An aneurysm is a ballooning of the wall of an artery resulting from weakening due to disease or other condition. Left untreated, the aneurysm may rupture, resulting in severe loss of blood and potentially death. An aneurysm in the abdominal aorta is the most common form of arterial aneurysm. The abdominal aorta, which extends downward from the heart in front of and parallel to the spine, through the thorax and abdomen, and branches off in a plurality of side vessels, connects the ascending aorta at the heart and to the circulatory system of the trunk and lower body. Branched vessels of the aorta supply the two kidneys via oppositely-directed renal arteries. Below the renal arteries, the abdominal aorta continues to about the level of the fourth lumbar vertebrae and divides at a Y-junction into the left and right iliac arteries, which supply blood to the lower extremities.
A common location for an aortic aneurysm is in the section of aorta between the renal and iliac arteries. Without rapid surgical intervention, a rupture of the abdominal aorta is commonly fatal because of the high volume of blood flow within the aorta. Conventional surgical intervention involves penetrating the abdominal wall to the location of the aneurysm to reinforce or replace the diseased section of the aorta. Typically, a prosthetic tube graft replaces the area of, or proximal and distal zones abutting, a potential rupture portion of the aorta. Unfortunately, conventional surgical intervention has resulted in substantial morbidity rates, and at the very least a protracted recovery period. Likewise, cost and other constraints militate for a longstanding need for endovascular intervention.
In recent years, methods and devices have been developed to treat an aortic aneurysm without opening up the abdominal wall. These new techniques typically involve a catheter-carried tubular graft delivered upward from the femoral artery through the iliac artery and into the region of the aneurysm. The graft normally includes a tubular graft body supported by an expandable stent, either self-expanding or balloon-expanding. The balloon-expanding type of stent naturally requires an expansion balloon, while the self-expanding type is simply deployed from the end of a tubular sheath. Implacement issues impact upon both known techniques.
If the aneurysm affects the Y-junction between the abdominal aorta and the iliac arteries, a bifurcated graft is typically used. A trunk portion of the bifurcated graft is secured to a healthy section of the abdominal aorta just below the renal arteries, and branched legs of the graft are secured within each of the iliac arteries, sometimes via a tubular extension graft. This procedure does not involve cardiopulmonary bypass, and thus blood continues to flow downward through the abdominal aorta. Certain complications arise in anchoring the graft to the inner wall of the vessel, because of the high blood flow both during the procedure and afterward. Indeed, the risk of grafts migrating within a vessel is a problem in many locations, not just in the abdominal aorta. In addition, the abdominal aorta may be aneurysmic very close to the renal arteries, which results in a fairly poor substrate within which to secure a repair graft. In fact, surgeons require various minimum lengths of healthy aortic wall below the renal arteries before an endovascular graft repair is indicated, or else a conventional invasive technique must be used. Moreover, the same consideration of a minimum healthy portion of the host vessel applies in other areas, especially with regard to the portion of the aorta adjacent the branching subclavian or carotid arteries. Additionally, leaking is likely to occur if a vessel is deformed due to an aneurysm.
A number of techniques have been proposed for anchoring grafts to vessel walls, most notably the use of barbs or hooks extending outward from graft that embed themselves into the vessel wall. Although these devices secure the graft, the intrusions into the vessel wall may damage the wall and cause complications. Alternatively, some devices have portions extending beyond the upstream end of the graft body which may be bent outward into contact with the vessel wall, either from a pre- or shape memory-bias, or from expansion of a balloon in this region. However, the optimal way to attach stentgrafts is to allow them to become naturally fixed to the vessels, such as by tissue ingrowth. This need is largely unaddressed in the art.
For example, the ZENITH AAA brand of Endovascular Graft from Cook, Inc. of Bloomington, Ind., utilizes an undulating wire support having barbs for supra-renal fixation of the graft. However, because these wires extend across the opening of the branching renal arteries they present a certain impediment to blood flow therethrough.
Moreover, any structure placed in the path of blood flow may tend to initiate the blood clotting cascade, which in turn, may generate free-floating emboli that would adversely impact the kidneys, or other organ that is perfused through the affected side branch. Because the kidneys are highly susceptible to injury from incursion of such emboli, it is highly desirable to avoid even the possibility of blood clotting at the mouth of the renal arteries.
In the context of preventing leaking around the graft, some manufacturers have provided grafts having texturized surfaces. For example, one such texturized graft is knitted, and includes a plurality of loops extending from the exterior surface of the graft. One known drawback associated with this configuration is that the knitted graft is, which is composed of loosely looped fabrics or threads, is very easily expansible. Such a graft may be subject to undesirable stretching and/or deformation within the body.
Another texturized graft is equipped with a plurality of loosely associated fibers, which may be affixed to or sewn to the exterior surface of the graft. Used appropriately, these configurations tend to reduce the incidence of leaking from around grafts in deformed vessels. However, neither of these texturized grafts sufficiently encourages tissue ingrowth into the graft. Such ingrowth is a natural bodily process that may be used to anchor the graft, and prevent undesirable migration.
Despite much work in this highly competitive field, there is still a need for a more secure means of anchoring a bifurcated graft in the abdominal aorta. More generally, there is a need for a more secure means of anchoring a tubular graft in a primary vessel, be it a bifurcated endoluminal prosthesis, an aorto-uniliac or any of the above.
The present invention uses xe2x80x98floaters,xe2x80x99 or specifically tailored threads integrated with the graft, which extend outside of the weave of the graft material. Such threads may be viewed as forming loops. These floaters may be formed from material similar to that used to form the graft, or may be formed from a material otherwise specifically tailored to promote tissue ingrowth. The floaters promote tissue ingrowth where they are placed along the exterior of the graft body. As such, they may be used to promote tissue ingrowth along the entire length, or at specific locations of grafts including, but not limited to, bifurcated grafts, aorto-uniliac grafts or thoracic LIFEPATH(copyright) AAA stent-grafts (Edwards Lifesciences, LLC, Irvine, Calif.).
According to a feature of the present invention there is provided an endoluminal graft having vertical, horizontal or angled filaments forming the floaters, the filaments ranging from at least about 1 cm to about 20 cm in length. Each filament may be woven into the graft material to form one or more floaters.
According to another feature of the present invention there is provided an endoluminal graft having vertical, horizontal and/or angled strands to promote tissue ingrowth along the length of an outer face of the graft member.
According to still another feature of the present invention there is provided an endoluminal graft having vertical, horizontal and/or angled strands to promote tissue ingrowth, and to resist migration, kinking, separation and perigraft blushing, or endoleak.
According to yet a still further feature of the present invention there is provided an endoluminal graft having vertical, horizontal and/or angled strands to promote tissue ingrowth along the length of an outer face of the graft member while providing a smooth inner surface for the reconstructed vessel lumen.
In a preferred embodiment, the present invention comprises a woven vascular graft adapted for placement in a primary blood vessel that is suited to bridge a vessel side branch, the graft having a texturized exterior surface designed to increase tissue in growth. The graft comprises a tubular structure defining an outer surface, a first portion of the outer surface being sized to contact and support the blood vessel on one side of the side branch, and a second portion of the outer surface being sized to contact and support the blood vessel on the other side of the side branch. The tubular structure defines an aperture for alignment with the side branch so as to permit blood flow between the blood vessel and the side branch.
In one embodiment of the present invention, the texturized exterior surface takes the form of plurality of horizontal, vertical and/or otherwise angled threads extending from the surface of the graft. Such exterior surface will be referred to as having xe2x80x9ctowelxe2x80x9d type threads. An alternate texturized exterior surface takes the form of a plurality of fibrous strands extending from the surface of the graft in a substantially angled, vertical or horizontal form with spaces for rows of threads skipped. Such exterior surface will be referred to as having a xe2x80x9cfibrousxe2x80x9d texture.
A still further alternate texturized exterior surface may have loose, vertical strands extending along the length of the graft surface. The integration of the texturized fibers with the woven graft in this manner serves to encourage the ingrowth of tissue from the wall of the blood vessel into the graft. Such ingrowth anchors the graft in position in the vessel and ensure compliance with morphology changes in the vessel over time, in addition to preventing kinking, migration or narrowing of the graft. It is known to those skilled in the art that empirical generation of a cellular matrix is promoted by having aspects or elements of a precursor to the cellular infrastructure which is to be created present at the situs of neointimal regeneration. With the present invention, the ability of the graft elements to seed and become incorporated into the cellular matrix ab inito has been show to promote a rapid and pervasive ingrowth.
The exterior surface of the graft may be designed to include a plurality of these surfaces. By way of example, the exterior surface may have a cuff, or extension portion, of towel type threads extending around the circumference of the ends of the graft. Such threads may have an angled orientation relative to the graft surface. The remainder of the exterior surface may be smooth. Alternatively, it may be covered with fibrous strands or loose vertical strands.
A preferred embodiment of the present invention is a bifurcated endoluminal prosthesis having a plurality of floater threaded portions separated by gaps or spaces along at least a substantial portion of the graft body.
An alternate preferred embodiment includes chevron-shaped, angled portions spanning predetermined aspects of an endovascular graft which may be an aorto-uniliac graft, a bifurcated graft or a thoracic graft.
In a further aspect, the invention provides a fibrously outer covered vascular graft system adapted for placement in a primary blood vessel and adjacent a vessel side branch. The system includes a tubular support graft including a first tubular structure sized to contact and support the blood vessel on one side of the side branch, and a second tubular structure spaced from and connected to the first tubular structure and sized to contact and support the blood vessel on the other side of the side branch. The system further includes a tubular primary graft sized to co-axially couple with the first tubular structure.
A further understanding of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings.